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How best to do the monoing, or summing, of the two signals?

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  • How best to do the monoing, or summing, of the two signals?

    Hi everyone.

    I'm building a small speaker with a 30w Dayton Audio ND91-4 (full Range) and a
    10W Dayton Audio ND16FA-6 (tweeter) with crossover.
    For an Amp I'm still in doubt between the
    Dayton Audio KAB-230 2x30W or the
    Dayton Audio KAB-250 2x50W
    1. In this the circuit,
      Click image for larger version

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      Some circuits eliminate the 10k resistor. What is the difference?
      And setting aside the values (presume they can only be calculated with the a known Amp impedance, that I don't) my question is: How much does the summing to Mono alter the amp power output?

    The two 30w channels became a 60w mono? (here is my doubt regarding which Amp to choose: The 30 or the 50W.

    2. Where does the crossover fit into? Before or after the summing?

    Thanks in advance for all the great Help

  • #2
    Try "mono amp" in the PE search box. You might find it easier going with one of the results, like this maybe:


    • #3
      That summing circuit will work fine, but it's for line level signals. You can't efficiently sum amplifier outputs. I would reconsider sticking with mono speakers, or look at mono amplifiers and a separate, summed Bluetooth adapter. Sent from my SM-G920P using Tapatalk
      Electronics engineer, woofer enthusiast, and musician.
      Wogg Music
      Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus


      • #4
        The KAB 2x50w board may still have issues (BT signal level, etc.). I believe the 2x30W board is more solid. Others can/will chime in on this issue.

        I don't believe the KAB boards have the provision/option to put the dual channel TPA board in mono mode (PBTL). And you won't get double the wattage by doing that with a given speaker. The max power ouput is governed by the PS voltage vis-a-vis the speaker impedance. The only power benefit mono gives you is the ability to drive a lower impedance (e.g. 2 ohm speakers). Since the impedance is lower at 2 ohms, you get more power for the any given PS voltage.

        The circuit depicted is good.


        • #5


          • #6
            The only other rec I can give is to make sure your fire insurance is up to date before you begin experimenting.


            • #7
              Can I ask why you particularly want a mono radio? I'm assuming it's for space purposes... makes sense.

              When I design a speaker crossover and am at the point of testing it out on real music (I do this I think as most do with just one speaker playing) the music often sounds funny as there are often stereo effects that don't translate well into being played by just one speaker. I can see why you'd want one speaker to play both L and R signals.

              With that amp, though, I don't know if it's possible. As has been said, I wouldn't try it after the amp, it's just a bad idea. Also, you could use that circuit on the input side of the line-in before the amp, but that will have no effect on the bluetooth portion, which I assume is important.

              The only thing I can think of is to modify your amp choices a bit and maybe use PE/Sure's high quality bluetooth board:

              Along with a suitable amp, such as this one... just use one channel; I'm sure there are probably better amps to pick from, but that one comes to mind and I've used it and it seems to work pretty well.

              You could wire your circuit right before the input to the amp, and use a switch before the circuit to select between the two sources, bluetooth or wired input.

              More complicated, but it may work out okay. Hopefully I didn't just steer you wrong, maybe some of the better "electrical" guys can double check my thinking.

              Oh Boy! I just re-read your post above. If you can get the signal to mono before sending it out to bluetooth then you have no issues at all. Just use one side of the amp, R or L and you should be fine. An amp not connected to a speaker has basically infinite impedance, so it's not going to hurt it one bit. Just pick a side and leave the other untapped. Problem solved.

              Sorry I didn't read more carefully!

              Zarbo Audio Projects Youtube Channel: * 320-641 Amp Review Youtube: *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
              *Part 2 *Gluing multiple curved laminations of HDF


              • #8
                Originally posted by JCM View Post
                ...Does a Amp feel comfortable with just one output connected?
                Never encountered an amp uncomfortable doing this.

                "Not a Speaker Designer - Not even on the Internet"
                “Pride is your greatest enemy, humility is your greatest friend.”
                "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."


                • #9
                  Note: if you are planning on a Bluetooth option, I would not use the KAB boards and their optional BT unit. You would have to modify the boards interconnect to sum the BT stereo signal into the board to get mono. That would not be an issue if your BT source has a mono mode.

                  I would use an stand alone amp and the Sure BT module. You can tie both the wired input and BT module output into the summer circuit for input into one of a stand alone amp's channels.

                  Many on this forum are happy with this amp:



                  • #10
                    Originally posted by Sydney View Post
                    Never encountered an amp uncomfortable doing this.
                    It is rare, but it can happen. I purchased a 2x50W sure amp a couple years ago that had its output filter corner frequency set around 16 kHz for some reason. I was testing it and I was driving both inputs, but only had one output connected to a load. When it would sweep through the L-C filter resonance point at 16 kHz, the output voltage would spike and the amplifier would go into protection mode for a few seconds. As I said, this is rare, but if you're going to leave the output disconnected, the best way to assure you won't have problems is to leave the input disconnected, or shorted for that channel.


                    • #11
                      Exceedingly rare: At least I'd never seen one, with decades of dealing with SS amps - including PA systems where amps are swapped in and used in such fashion.
                      Doesn't preclude the existence of faulty or less than robust designs however
                      "Not a Speaker Designer - Not even on the Internet"
                      “Pride is your greatest enemy, humility is your greatest friend.”
                      "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."